Periodontal disease and dental caries are of major public health and economic interest worldwide. It is now widely recognized that both of these oral diseases are caused by bacteria which grow in masses on the teeth and in the gingival area. A commonly used descriptive term for these bacterial masses is "dental plaque". In the case of periodontal disease, Schluger et al. (Schluger, Yuodelis, Page & Johnson, Periodontal Diseases, second edition, pp. 153-262, Lea & Febiger, 1990) report that dental plaque bacteria, growing in the area where the teeth and gingival tissues meet, cause an inflammation of the gingiva called "gingivitis". This is characterized by swollen, edematous gingiva ("gums") which are reddened and bleed easily. If plaque removal is inadequate, gingivitis may progress to "periodontitis" or periodontal disease in many individuals. Periodontitis generally is a characterized by a chronic inflammation of the tissues around the teeth, which leads to a resorption of supporting bone. Periodontal disease is the leading cause of tooth loss among adults. Dental caries (cavities) are also caused by bacteria, with Streptococcus mutans being the principal etiologic agent (McGhee, Michalek & Cassell, Dental Microbiology, p. 279, Harper & Row, 1982).
The prevention of dental plaque or the removal thereof has long been the focus of development, with the ultimate goal of inhibiting both caries and periodontal diseases. While the formation of dental plaque can be inhibited to a certain extent by brushing the teeth at frequent intervals, brushing along is not sufficient to effectively prevent the formation of dental plaque or remove substantially all of the dental plaque that has formed on the teeth. Since brushing alone is often not sufficient to prevent dental caries or periodontal disease due to pathogenic plaque bacteria, chemical methods using anti-bacterials such as chlorhexidine, benzalkonium chloride, and cetylpyridinium chloride have been proposed.
The use of natural products for the treatment of teeth and gums is old in the art, having been practiced and documented since the mid-1880s. Since then, many patents have disclosed compositions of oral products containing natural product extracts.
It is known that hinokitiol, citral, geraniol, cocamidopropyl betaine, berberine, and juniper berries oil, individually exhibit antimicrobial properties against certain bacteria.
U.S. Pat. No. 3,940,476 describes a method for inhibiting the formation of dental plaque, which comprises topically applying to the teeth as an active ingredient an amount of either one or a combination of (a) allyl isothiocyanate, (b) uranine, (c) obtusastyrene, (d) citral, (e) citronellol, (f) nerol, or (g) geraniol.
U.S. Pat. No. 4,913,895 describes an oral composition including a linear polyphosphate or a cyclic polyphosphate and menthol, anethol, or mixtures thereof in an aqueous medium. The composition is reported to have antibacterial effects and prevent the development of calculus and periodontal diseases.
U.S. Pat. No. 4,966,754 describes that certain essential oils and combinations thereof possess antimicrobial properties against Aspergillus niger, Candida albicans, Staphylococcus aureus, and Pseudomonas aeruginosa and therefore are useful as preservatives in cosmetic compositions. A blend of 14 essential oils is described as providing desirable antimicrobial properties against the noted microorganisms. The described combination is disclosed as being suitable as a preservative for cosmetic compositions.
U.S. Pat. No. 4,999,184 describes oil compositions containing certain pyrophosphate salts which are reported to provide an anticalculus benefit.
U.S. Pat. No. 5,316,760 describes a mouthcare product that contains a combination of Urtica dioica extract and an extract of Juniperus communis. The combination of these extracts is described as leading to a synergistic reduction of both dental plaque and bleeding or inflammation of the gingiva. Achillaea millefolium extract is also described as being a suitable additive to the combination of the Urtica dioica and Juniperus communis extracts.
U.S. Pat. No. 5,472,684 describes a composition including thymol and eugenol, and optionally a sesquiterpene alcohol, such as farnesol, that reportedly has antiplaque and antigingivitis effects. Australian tea tree oil, sage oil, and eucalyptol are described as enhancing the antiplaque and antigingivitis activity of mouth rinses formulated from the disclosed compositions.
One property that characterizes the effectiveness of an antimicrobial agent as an antiplaque and anticalculus agent is the minimum inhibitory concentration, or MIC, of the agent. The MIC is the minimum concentration in micrograms per milliliter of an antimicrobial agent at which no bacterial growth is observed. At concentrations below the MIC, an antimicrobial agent is ineffective at killing or inhibiting the growth and reproduction of bacteria. At concentrations above the MIC, an antimicrobial agent is effective at killing or inhibiting the growth and reproduction of bacteria.
Typically, antimicrobial agents are introduced into the oral cavity at an initial concentration. Almost immediately, the initial concentration begins to decrease due to the dynamics of the oral cavity. Eventually, the concentration of the antimicrobial agent within the oral cavity will fall below the MIC. Thus, it has been a goal of those working to develop antiplaque and anticalculus formulations to use antimicrobial agents that have low MICs.
Chlorhexidine has a MIC of about one .mu.g/ml and is the standard against which other antimicrobial agents are measured. While chlorhexidine has a desirable MIC, it also exhibits undesirable taste and has the undesirable side effect of staining teeth.